The present invention relates to a heat pipe in the form of a container having water enclosed therein as a working fluid and made of iron, copper or the like which reacts with water to evolve hydrogen gas.
The term "iron" as used herein includes pure iron and also iron alloys such as stainless steel and carbon steel.
Heat pipes comprising an iron container having water enclosed therein as a working fluid are in wide use because of the high strength of the container and the high performance of water as the working fluid. However, such heat pipes have the problem that iron reacts with water to evolve hydrogen gas, impairing the performance of the heat pipe in a short period of time. More specifically, the evolved hydrogen gas diffuses through the wall of the container in the form of atoms and becomes partly released from the container at a constant rate, but a major portion of the hydrogen gas remains in and occupies the condensing portion within the container to impede condensation of vapor and lower the performance of the heat pipe. Such impairment becomes pronounced with time, rapidly shortening the life of the heat pipe. While the iron container is sometimes aluminized over the outer surface to provide protection against corrosion and also to attach thereto aluminum fins having a brazing layer formed by vacuum brazing, the hydrogen gas diffusing through the container wall is then prevented from escaping from the container by the aluminized coating.
Accordingly, the following means have heretofore been employed to prevent the evolution of hydrogen gas and to preclude deterioration of the heat pipe due to the evolution of hydrogen gas.
(1) Addition of an inhibitor to the working fluid, i.e. water, to inhibit the reaction between water and iron.
(2) Plating of the inner surface of the iron container with copper or like metal.
(3) Provison of a hydrogen occluding material within the container.
(4) Provision of a linear hydrogen passing member of Pd, or use of hydrogen-permeable Pd for forming the condensing portion to hold the interior of the container in communication with the outside.
However, the means (1) and (2), if used, are unable to inhibit the evolution of hydrogen gas, while the means (3) and (4) fail to fully occlude or release hydrogen gas when the heat pipe is used as high temperatures which result in evolution of an increased amount of hydrogen gas. Accordingly, it has been impossible to prevent the heat pipe from deterioration even with the use of means (1) to (4).